Explanation: A bypass capacitor's fundamental purpose is to divert unwanted alternating current (AC) or radio frequency (RF) signals away from a desired circuit path, typically to ground. It achieves this by offering a very low impedance path to ground for AC signals, while simultaneously presenting a very high impedance (ideally infinite) to direct current (DC). This effectively shunts AC noise or ripple current, ensuring a stable DC voltage or isolating AC signals. Option A is incorrect; bypass capacitors are not primarily used for changing the resonant frequency of a circuit, although they can be part of frequency-dependent filters. Option B is incorrect; a capacitor blocks DC, it doesn't shunt DC to ground. Its *purpose* in this context is to remove AC. Option D is incorrect; impedance transformation is usually accomplished with transformers or specific matching networks, not a simple bypass capacitor.